1. Field of the Invention
The invention relates generally to respiration monitors and, in particular, to a self-contained apnea monitor for use at home or in a hospital.
2. Description of Related Art
Apnea, the transient cessation of breathing, is a significant health problem. Apnea most often occurs during sleep and is often undetected. Apnea during sleep is commonly called "sleep apnea."
In a mild form of sleep apnea, a person temporarily stops breathing during the night, often several times. Each individual instance of a cessation of breathing is referred to as an "apnea event," and such events are deemed to occur when breathing stops for at least 20-35 seconds.
Left untreated, mild sleep apnea can result in, e.g, excessive tiredness during the day, an irregular heartbeat at night, anxiety, depression, or an inability to concentrate, including a possible loss of memory. In its more serious forms, sleep apnea can result in death, particularly for infants. Recent research has shown that apnea may be a leading cause of Sudden Infant Death Syndrome.
Generally, sleep apnea takes three forms: obstructive sleep apnea, central sleep apnea, and mixed sleep apnea. In obstructive sleep apnea, structures in the throat block the flow of air to and from the lungs, or the obstruction may be caused by a foreign object lodged within the airway. Central sleep apnea occurs when the brain does not send out necessary signals to continue breathing, i.e., the person simply "forgets" to breathe. Mixed sleep apnea is a combination of both obstructive sleep apnea and central sleep apnea.
Another breathing phenomena, closely related to apnea, is "periodic breathing" or "shallow breathing." Shallow breathing occurs due to a lack of breathing volume over an extended period of time, perhaps 15-20 minutes or more. Due to a lack of adequate breathing volume, blood oxygen saturation levels become depleted, leading to a "hypoxic" state. With apnea, breathing merely ceases, quickly leading to hypoxia. With shallow breathing, oxygen depletion is more gradual. Many conventional apnea monitors are not equipped to detect hypoxia resulting from shallow breathing.
Numerous devices have been designed to detect apnea events, either for the purpose of diagnosis or for the purpose of alerting a physician or parent that an apnea event is occurring such that the patient may be revived as necessary. Such devices detect or measure one or more aspects of breathing including: respiration, heart rate, oxygenation or ventilation. Respiration monitors detect either actual airflow to and from the lungs by means of a mouth or nasal thermistor, or by means of a carbon dioxide detector. Alternatively, the monitors detect an effort at breathing by means of electrical activity sensors having electrodes for measuring skin impedance or inductance. Heart rate is typically measured using a continuous ECG or a cardio-tachometer. Oxygenation and ventilation are detected through transcutaneous oxygen tension and saturation and transcutaneous carbon dioxide, respectively.
Exemplary respiration monitors are disclosed in U.S. Pat. No. 4,576,179 to Manus et al., U.S. Pat. No. 4,433,693 to Hochstein, and U.S. Pat. No. 3,782,368 to Reibold.
Manus et al. discloses a respiration monitoring apparatus mounted on a belt for encircling the thorax of a patient. A piezoelectric crystal is mounted within the device such that outward extension of the thorax causes a bending or deformation of the piezoelectric crystal, thus producing an electrical signal which is monitored.
Hochstein also discloses a respiration monitoring device mounted on a belt for encircling the thorax of a patient. The device includes an oscillator for generating an electromagnetic field having an output frequency in the radiofrequency range, and further includes a high Q passively-tuned LC circuit, which has a resonant frequency variable in the radiofrequency range generated by the oscillator. These devices are positioned on the belt encircling the patient's thorax such that expansion of the thorax varies the resonant frequency of the LC circuit. Extension of the thorax is thus detected when the resonant frequency of the LC circuit corresponds with the frequency of the electromagnetic field generated by the oscillator.
Reibold discloses a monitor including a moment actuated transducer unit mounted to an elastic belt for encircling the thorax of a patient. The moment-actuated transducer includes a piezoelectric element having a predetermined capacitance. The piezoelectric element is connected to the belt by a pair of bending arms such that expansion of the thorax bends the bending arms and, thus, deforms the piezoelectric element. Means are provided to detect an electrical signal output from the piezoelectric element.
Related devices are disclosed in U.S. Pat. No. 3,996,922 to Basham, U.S. Pat. No. 3,638,642 to Heflin, Sr., U.S. Pat. No. 4,630,614 to Atlas, U.S. Pat. No. 4,671,297 to Schulze, Jr., U.S. Pat. No. 4,648,396 to Raemer, U.S. Pat. No. 4,580,575 to Birnbaum et al.. U.S. Pat. No. 4,625,733 to Saynajakangas, U.S. Pat. No. 4,595,016 to Fertig et al., U.S. Pat. No. 4,546,778 to Sullivan. U.S. Pat. No. 4,509,527 to Fraden. U.S. Pat. No. 4,506,678 to Russell et al.. U.S. Pat. No. 4,478,224 to Bailey, U.S. Pat. No. 4,475,559 to Horn, U.S. Pat. No. 4,444,201 to Itoh, U.S. Pat. No. 4,417,589 to Favaloro. U.S. Pat. No. 4,414,982 to Durkan. U.S. Pat. No. 4,365,636 to Barker, U.S. Pat. No. 4,350,166 to Mobarry, U.S. Pat. No. 4,289,142 to Kearns. U.S. Pat. No. 4,146,885 to Lawson, Jr.. U.S. Pat. No. 3,802,417 to Lang, U.S. Pat. No. 3,882,847 to Jacobs, and U.S. Pat. No. 3,713,436 to Hardway, Jr.
The apnea detectors and monitors of the prior art are generally expensive, and may be unreliable, and difficult to use. Many require training to operate and constant supervision to maintain.